1. Field of the Invention
This invention relates to a subject tracking apparatus, and more particularly, is applicable to a system in which a subject can be automatically photographed in a camera with VTR, a camera for business, a television conference system, a videophone, a security system, and the like.
Further, this invention is applicable to a camera for photographing a subject in the best condition by controlling auto-iris or auto-zoom in a camera in accordance with the information of the subject.
Also, this invention is applicable to an automatic editing system for taking out only a scene of which a subject is photographed, and enables efficient cording which gives much information to a subject.
2. Description of the Related Art
Heretofore, there have been many kinds of systems which track a subject from the sensor information other than a camera (image).
In the above systems, a subject tracking apparatus has been proposed, in which a subject to which a signal transmitter of infrared rays or supersonic waves is attached, and the signal is received at a sensor to detect the direction from the change of level of received signal or phase difference. As a method that a special signal transmitter is not needed, a subject tracking apparatus has been proposed, in which a combination of voice and stereo microphone, pyroelectric sensor, and the like are used so as to detect the direction from the received signal of sensor similar to the above method.
Also, as a system for tracking a subject based on the color video signal, for example, the following four relating application have been proposed by the same applicant: U.S. Pat. No. 5,355,163; European Patent Laid Open No. 0561593 (Published Date: Sep. 22, 1993); European Patent Laid Open No. 0578508 (Published Date: Jan. 23, 1994); and European Patent Laid Open No. 0634665 (Published Date: Jan. 18, 1995). (In addition, the U.S. Patent Applications corresponding to three European Patent Laid Open Numbers are now in pending. Each of the above applications is owned by the assignee of the present invention and is hereby incorporated by reference.)
Heretofore, in such type of the subject tracking apparatus, the movement of a target object in the picture photographed by the television camera is detected so as to realize the automatic tracking in the photographed direction. Block matching is commonly used in the detection of the movement. Here, block matching is the method for detecting the block of which the correlation with the original block defined by the surroundings of the target or the characteristic part of the picture becomes maximum among the photographed pictures, and for detecting the position of block where the absolute value sum of the difference of pixels between the original block and that block becomes minimum as the the position of the target.
However, in the subject tracking apparatus using the block matching method, the target position is determined depending on the information of shapes contained in the original block. Therefore, it has been a problem that tracking becomes difficult in the case where the target changes its shape or its size. Moreover, since the processing to calculate the absolute value of difference of pixels between the original block and the block in the image requires numerous calculation works, it has been a problem that the circuit construction becomes complicated and it is difficult to realize by means of micro-computer.
Hence, a subject tracking apparatus to track the target by using the information having color video signal has been proposed (Japanese Patent Application No. 61060/1993).
The subject tracking apparatus tracks the object regarding the area as the target, the area being adjacent to the area detected the last time, i.e., time continuity of image obtained by integrating color image in the horizontal direction and the vertical direction respectively based on the fixed color making this color as the feature quantity.
Similarly, another subject tracking apparatus to track the object by using color video signal has been proposed (Japanese Patent Application No. 261678/1993).
The subject tracking apparatus comprises means for modeling the color of target from the color difference of the target (that is, R-Y signal and B-Y signal) by the linear function, and means for modeling the luminance Y and the saturation S of the target by the linear function. The estimated coefficient obtained from two means is feature quantity.
In the subject tracking apparatus, an evaluation function in the horizontal/vertical directions is respectively made from the difference between the data to be calculated from the estimated coefficient and the actual data, and the target tracking is conducted depending on this evaluation function.
However, in case of the subject tracking apparatus, since the color of the target is approximated by the linear function, the model error becomes bigger in accordance with the deviation of hue due to the luminance change and it becomes difficult to detect the feature quantity.
Hence, as an subject tracking apparatus has been proposed, in which means for modeling the luminance Y and the saturation S of the target by the linear function is replaced to means for modeling them by the quadratic function. The apparatus can heighten the modeling efficiency of the target color as compared with the above method and can improve the tracking ability of the target.
However, in this case, the color setting is so strict that the identification of the target may become difficult. Thereby, some error must be estimated with respect to model. Since it is difficult to set the quantity of error, there is a problem that the color of target can not be distinguished from the color of background if much quantity of error is estimated. Moreover, the target having colorless can not be distinguished.